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May be a stupid question, how close between OPT and 845 can be

155.137.212.50
Posted on May 24, 2022 at 23:57:03
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001



Hi folks,

By using Lundahl OPT transfomer which has no external housing, if I place OPT next to 845 tube, how close (minimum distance) can I place them in order not to get the OPT terribly heated up to unacceptable level. Is 35mm enough?

Your comment ?

 

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I think it is too close. Unless you use a shield...nt, posted on May 25, 2022 at 00:37:10
Bas Horneman
Audiophile

Posts: 4084
Joined: March 28, 2001
 nt

 

RE: I think it is too close. Unless you use a shield...nt, posted on May 25, 2022 at 01:23:55
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 Rule of thumb is at least the diameter of the tube but that is when the windings are still covered by a transformer bell.

If you want to go closer you might be in luck:
Go over to parts connexxion and buy a Pearl tube cooler for the 845. Pearl-HiFi has closed up shop but there are still some models around for purchase.

They are not the strongest item, I would suggest that you get 4 in case you damage one (and then still have one spare). (Skinny EL34 and 6SN7 have sold out, I wanted some and discovered Bill Perkins closed shop)

https://www.partsconnexion.com/ACCESS-64470.html

I have some that are about 2/3rds of the diameter away from a shielded transformer with the Pearl tube coolers and it is OK. Make sure you've got holes around the base for ventilation.

I wish I had followed my own advice as I bought only two.... When I buy tubes and need only a pair I normally buy 5 (in the past there were 5 in a "sleeve"): two pairs and one for a dud or early failure. If you have even the slightest thoughts of building a second one then by all means get 5, once they are gone they are gone never to return. The upshot of these coolers is that US Military tests have shown considerable increase of life exp[ectancy when tubes run cooler and at the price of the 845 they will pay themselves back with a single pair's extended life.

 

RE: May be a stupid question, how close between OPT and 845 can be, posted on May 25, 2022 at 05:46:43
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 You're asking for a hernia. Split that in two.






 

Effect of a tube cooler on adjacent tubes?, posted on May 25, 2022 at 08:19:15
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 Since a tube cooler enhances the radiation of heat away from the tube, could that be bad for adjacent small signal tubes in the vicinity? And if you put a tube cooler on the adjacent tubes, where does the heat go? Or how would you handle the situation?

 

RE: Effect of a tube cooler on adjacent tubes?, posted on May 25, 2022 at 09:02:49
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 Radiation is absorbed by the cooler and that cooler gets cooled by air draft from bottom to top. Nearby tubes run cooler. Pearl-HiFi.com has quite some documentation on this. KH6GRT has a web page on IERC heat shields.

For my noval drivers I actually prefer the original IERC coolers but they get now far and few between offered for sale.

Unfortunately some 12A?7 are slightly fatter and don't fit the IERC coolers but it is hardly an issue for those tubes since they run normally cool. But if needed shielding then one of those bare aluminium cans will raise the temperature considerably and it is better to use an IERC. Unfortunately the Pearl HiFi coolers do not work in the capacity of shielding.

There was some discussion on this some time ago on audiokarma where tests done by one participant showed very similar results (IIRC) between the latest IERC version and the Pearl HiFi versions.

 

RE: Hernia, posted on May 25, 2022 at 09:12:04
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 I agree with Triode Kingdom, split them in two, you've got already two mains transformers and chokes by the looks of it and the only thiong missing is an extra meter.

18 months ago I could lift 30kgs but now I'm struggling to lift 10 kgs - anything more and I run the risk of another collapsed vertebrae due to osteoporosis.(Added three since the start of this year, ouch... Not getting any younger.)

 

Thanks for that information..., posted on May 25, 2022 at 09:13:26
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 The 7241 power triodes in my OTL amplifiers are only a few inches away from the input stage tubes, so I would want to be sure that putting a cooler on the 7241s will not adversely affect the much smaller tubes nearby. Using the thermal probe on my Fluke meter, I once measured a temp of 100 degrees C on the surface of a 7241, which was passing barely 50W of its 100W max capacity at idle.

 

RE: Thanks for that information..., posted on May 25, 2022 at 11:32:56
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 If it is only 100C then I would not worry too much - it is a different situation when the tube is running at maximum dissipation andthe glass temperature gets around the 220C.

It has to do with the Kelvin temperature of the cathode which should stay within a narrow band. Cannot remember where I read all the details otherwise I would point you in that direction.

But for rare and/or expensive tubes it may be worthwhile to use. I am having a pair of EL506 (the last iteration of the 7868 with half the distortion of the 7868/7591) and good luck finding a pair of those. I've 4 four pairs of 7868, two pair are NOS the others I don't know. But the 7868 are Novar whereas the EL506 are Magnoval so it means a socket change if one of the EL506 goes belly-up.

I'm using slow ramp up of the filament and then slow ramp up of B+, every hour extra that I can squeeze out helps. Same as that I am running my amplifier at design ratings and not at absolute ratings what many manufacturers do (and shorten tube life).

I've also stocked up with the 12AT7 driver: got five NOS Telefunken ECC81's and three NOS Brimar E81CC. Fortunately all bought before the short supply of new tubes.

 

+1, posted on May 25, 2022 at 17:33:02
Stephen R
Audiophile

Posts: 1428
Joined: January 11, 2002
 I split the individual channels in half again, lower psu, upper audio so I can work on them and when combined, they live on casters.

 

RE: Hernia, posted on May 26, 2022 at 06:15:47
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 Hi 7868 and Triode Kingdom

I suffered stroke in 2022, my right hand paralyzed since then and I can't speak very well too, I can't even lift 10kg, to lift up the amp I might get some help but to solder the amp circuit more or less only rely on myself. I can use left hand to hold soldering iron while my lips grip the solder wire. I now use many solid tape and a Vice to fix the subjects before I solder.Yes, take almost 10 time more time to do the job

before the stroke I was a project manager for metro construction projects covering south America and Asia countries, yes I traveled a lot, but now nothing. The thing I still want to do is to build tube amp, better than staying at home doing nothing

Building this integrated 845 amp has been my goal because I always want a simplest 3-tube application(4 stage tube), and I always find that 1st and 2nd stage using direct couple is the edge in integrated amp as the 2nd stage is >1m ohm input impedance. This is obviously an advantage over preamp + power amp, because I can use more cathode degeneration to make 1st stage more linear and it has no sonic drawback of loop NFB. I do not like loop NFB at all

The two main power transfomers are not the same, one purely 960V AC. The other one is 340V AC with all the tube filament supply, because I use silicon rectifier for high voltage. The tube filament first power on then after 1 minute the NE555 switch on the 960V AC transfomer.

 

RE: Hernia, posted on May 26, 2022 at 06:22:51
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 typo, I suffered stroke in 2020

 

Make a separate chassis for the power supply, posted on May 26, 2022 at 06:31:01
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Not only does it cut down the weight for your amp but it would lower the noise floor by putting the AC components further away from the sensitive amplification stage. You can also hide the power supply chassis for a "cleaner" look.

 

HV, posted on May 26, 2022 at 07:12:03
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 I thought about that during the initial design of my own SETs. Running that much HV through an umbilical was problematic. I've owned Ham gear that did this with as much as +750V using octal sockets. However, my SETs produce nearly +1,100V for the output stage anodes. That's too much for octals, so two umbilicals would have been required. In the end, I decided to split it into monoblocks. Even so, they're shaping up to be about 70-80 lbs each.

Regarding noise, this shouldn't be an issue for line-level power amps. Even my last guitar amp was quiet, and it uses several cascaded 12AX7s. Much more gain and sensitivity than a hi-fi amp. For a large SET, good design will prevent this from being a problem, even with high efficiency speakers.



 

Casters - I Like It!, posted on May 26, 2022 at 07:14:22
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 Great idea! Now I just need a crane and pulley system to get them up and down the stairs while I'm working on them...




 

RE: Hernia, posted on May 26, 2022 at 07:36:35
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 It sounds like you're seriously handicapped, sorry to hear that. Have you attempted to find other builders in HK who might be willing to help out? I used to visit mainland China frequently, but I don't know much about the audiophile culture where you are.

 

Are the Pearl coolers elasticized?, posted on May 26, 2022 at 07:58:50
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 The salient question is my 7241s are 57mm in diameter. Should I order the coolers to be a bit less in diameter, for a snug fit?

 

RE: Make a separate chassis for the power supply, posted on May 26, 2022 at 08:01:59
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001



Something like this, but the HV cable scare me a little, how can we make it safe, should they be two separate cables for HV and filament ?

 

RE: Make a separate chassis for the power supply, posted on May 26, 2022 at 08:24:03
DAK
Audiophile

Posts: 2712
Location: PACIFIC
Joined: August 8, 2010
 Yes you can make a separate shielded cable for the filament supplies that is grounded only on one of the chassis. I also ran a seperate ground cable with the filament wires. Then run the high voltage using suitable rated high voltage wire. I used cinch connectors for the ends which are rated for this type of use. You can buy a woven wire cover to pretty it all up or use cable loom or split loom to hide the different wires. I used shrink wrap on mine but that makes the cable rather stiff.

 

RE: HV, posted on May 26, 2022 at 08:24:05
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001
 >>Even so, they're shaping up to be about 70-80 lbs each.

Why so heavy? Any reason?


I have been considering what components actually contribute the weight to the amp, well mainly the transformers and the chassis.

The integrated 845 I gonna build has two lundahl C Core OPT total weight 9.6kg pair, two EI main power 5.5kg each x2, 2 interstage tyranny 1.5kg for 2 pcs., two chokes are 2kgs.

Altogether the 24kg tyranny plus 9kg chassis (top plate 6mm thick Aluminum + wooden bottom chassis), all other components may weigh another 4kg, so I expect 37kg total.

 

RE: Are the Pearl coolers elasticized?, posted on May 26, 2022 at 08:27:52
2chblast
Audiophile

Posts: 196
Location: Calgary
Joined: February 7, 2004
 Yes they are elasticized. They have upgraded from standard rubber to silicone O-rings so they don't dry out and break. Got a new set of silicone rings for the cost of shipping. They work great and have increased the life of the output tubes on my Eico HF-81 greatly.

 

Weight, posted on May 26, 2022 at 08:48:09
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
Each power supply chassis weighs about 11.5 kg. The components on the main chassis are about the same (mostly the Magnequest OPT). Then there's the chassis itself, which is made of 6mm aluminum side and top panel, and a 13mm front panel. I don't know how much the chassis itself weighs, but it's heavy.









 

Does a layer of glass help to mitigate the heat radiation ?, posted on May 26, 2022 at 09:15:04
Eric Chan
Audiophile

Posts: 368
Joined: October 31, 2001



I am thinking of putting a piece of glass to form the housing, like the picture

Does a layer of glass help to mitigate the heat radiation ?

 

the Pearl coolers will fit different diameters, posted on May 26, 2022 at 15:36:01
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 The Pearl coolers will fit different diameters but you will need to get some different diameter silicon O-rings.

Have a look at https://audiokarma.org/forums/index.php?threads/new-build-kegger-seul-el84.992346/page-4#post-15581049

I would get the one whichever one is the closest in diameter. If there is only minimal difference between the oversize / undersize difference each with the tube then my preference would be for the larger (ending up with more fins = better cooling). Put the O-ring on before sliding it on the tube.

Cheers!

 

RE: Make a separate chassis for the power supply, posted on May 26, 2022 at 16:04:01
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 Check out the different coax cables and connectors. e.g. a N-connector will withstand (if I remember correctly) 5 kV. Some coax is better than others, you can buy coax made from Teflon that will withstand even higher voltages. (the horror plastic - if does not break down in nature so use it sparingly)

 

RE: Does a layer of glass help to mitigate the heat radiation ?, posted on May 26, 2022 at 18:32:20
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 The infra-red heat radiation will straight go through the glass. After all that is the heat coming from the tubes' anodes goes out through the tubes' glass.

The transformers will heat up as a result of the DC current going through their windings - there are ventilation holes visible in the top.

You should have good machining firms in HK that can make your chassis, otherwise landfallsystems.com in the USA can make a chassis for you.

PS I lived in Hong Kong around the turn of the century (Happy Valley) and enjoyed your city very much. Don't know how much it has changed in the last 20 years, would like to visit again but health prevents me.

 

RE: Weight, posted on May 26, 2022 at 18:48:35
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 Current amplifier is approx. 11 Kgs. Chassis is made from 1/8" (3mm) aluminium top and sides, bottom is 3/32" (2mm), and it weighs around 2.7 Kgs. (output transformers ea. 2.1 Kgs, mains 2.7Kg, choke 1.1Kg)

If mains transformer is mounted flat use extended bolts and mount on silicon rubber washers - takes the hum away out of the chassis. I distributed the weight so each corner would be about the same load. Then used some silicon rubber feet used in computers to stop noise transfer to the desk. Inaudible. https://www.quietpc.com/components?q=feet

 

RE: +1, posted on May 30, 2022 at 17:25:01
dave slagle
Manufacturer

Posts: 5430
Location: NYC
Joined: April 27, 2001



It is all about the wheels....

 

LOL, posted on May 30, 2022 at 20:39:25
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 I used to have a 4KW RF linear amplifier that looked like that. It was a health hazard to the entire community.




 

RE: +1, posted on May 30, 2022 at 21:02:42
7868
Audiophile

Posts: 82
Location: Wairarapa
Joined: March 4, 2022
 And he's lying underneath to check the HT voltage.....

 

Be careful with that thing...., posted on June 1, 2022 at 11:17:37
Lew
Audiophile

Posts: 10912
Location: Bethesda, Maryland
Joined: December 11, 2000
 You may find yourself in a parallel universe if you get to close.

 

Update..., posted on June 2, 2022 at 09:56:47
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 I installed a PS plate into one of the main chassis yesterday. After weighing it this morning, I believe total amplifier weight after the remainder of the components are installed will be about 60 lbs (27 Kg). That's less than my previous estimate, but I feel every bit of this when I pick up the chassis.



 

60lbs, posted on June 6, 2022 at 18:50:46
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 I believe that's what a HK Citation 2 weights.

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: 60lbs, posted on June 11, 2022 at 23:11:03
Triode_Kingdom
Audiophile

Posts: 10047
Location: Central Texas
Joined: September 24, 2006
 So the Citation II weighs 0.5 lb per watt. These amps are 2 lbs per watt. IOW, half the power and twice the weight. LOL, someone tell me why I did this again...


 

LOL nt, posted on June 12, 2022 at 17:08:26
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 .
Have Fun and Enjoy the Music
"Still Working the Problem"

 

5.5 watt mono block, output stage only, posted on June 13, 2022 at 10:11:23
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002



I'm not sure what it weighs but a lot more that 2 pounds per watt. :-)

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

53 pounds divided by 5.5 watts = 9.64 pounds per watt!!! nt, posted on June 13, 2022 at 14:20:49
Tre'
Industry Professional

Posts: 17302
Location: So. Cal.
Joined: February 9, 2002
 And the driver stages are on their own stereo chassis and the power supply for that on it's own chassis.

If you put the whole thing together it would be a very large and heavy, four chassis, 5.5 watt per channel stereo amplifier.


Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"

 

RE: May be a stupid question, how close between OPT and 845 can be, posted on June 16, 2022 at 07:03:38
Naz
Audiophile

Posts: 2184
Location: Sydney
Joined: September 2, 2005
 35mm is enough IMO but I wouldn't want to go any closer. And I agree that a pair of monoblocs makes more sense than an integrated for a serious build with quality iron and decent chokes (meaning heavy), which are a must for good sound.

Naz

 

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